Method and apparatus for constructing very high throughput long training field sequences

ABSTRACT

Certain aspects of the present disclosure relate to techniques for constructing a training sequence as a part of transmission preamble in an effort to minimize (or at least reduce) a peak-to-average power ratio (PAPR) at a transmitting node.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims benefit of ProvisionalApplication Ser. No. 61/321,330 filed Apr. 6, 2010, ProvisionalApplication Ser. No. 61/321,752 filed Apr. 7, 2010, ProvisionalApplication Ser. No. 61/323,775 filed Apr. 13, 2010, ProvisionalApplication Ser. No. 61/332,360 filed May 7, 2010, ProvisionalApplication Ser. No. 61/333,168 filed May 10, 2010, ProvisionalApplication Ser. No. 61/334,260 filed May 13, 2010, ProvisionalApplication Ser. No. 61/348,349 filed May 26, 2010, ProvisionalApplication Ser. No. 61/350,216 filed Jun. 1, 2010, and ProvisionalApplication Ser. No. 61/354,898 filed Jun. 15, 2010, and assigned to theassignee hereof and hereby expressly incorporated by reference herein.

CLAIM OF PRIORITY UNDER 35 U.S.C §120

The present Application for Patent is a continuation-in-part of patentapplication Ser. No. 12/731,634 filed Mar. 25, 2010, pending, whichclaims benefit of Provisional Application Ser. No. 61/226,615 filed Jul.17, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

BACKGROUND

1. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to a method and apparatus forconstructing a long training field (LTF) sequence as a part oftransmission preamble for Very High Throughput (VHT) wireless systems.

2. Background

The Institute of Electrical and Electronics Engineers (IEEE) 802.11 WideLocal Area Network (WLAN) standards body established specifications fortransmissions based on the Very High Throughput (VHT) approach using acarrier frequency of 5 GHz (i.e., the IEEE 802.11ac specification), orusing a carrier frequency of 60 GHz (i.e., the IEEE 802.11adspecification) targeting aggregate throughputs larger than 1 Gigabitsper second. One of the enabling technologies for the VHT 5 GHzspecification is a wider channel bandwidth, which bonds two 40 MHzchannels for 80 MHz bandwidth therefore doubling the physical layer(PHY) data rate with negligible increase in cost compared to the IEEE802.11n standard.

A VHT Long Training Field (LTF) is a part of a transmission preamble,and can be utilized at a receiver side to estimate characteristics ofunderlying multiple-input multiple output (MIMO) wireless channel.Methods and apparatus are proposed in the present disclosure forconstructing the VHT-LTF sequence, while providing a low peak-to-averagepower ratio (PAPR) at a transmitting node.

SUMMARY

Certain aspects of the present disclosure support a method for wirelesscommunications. The method generally includes constructing a longtraining field (LTF) sequence of a preamble by combining a plurality ofinterpolating sequences with LTF tone values associated with at leastone of the IEEE 802.11n standard or the IEEE 802.11a standard, whereinthe LTF tone values cover at least a portion of bandwidth of a firstsize, and each of the LTF tone values is repeated one or more times fordifferent subcarriers, rotating phases of tones of the LTF sequence perbandwidth of the first size in an effort to reduce a peak-to-averagepower ratio (PAPR) during a transmission of the LTF sequence, andreplacing tones of the LTF sequence at pilot locations with a definedstream of values chosen in an effort to reduce the PAPR.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a firstcircuit configured to construct a long training field (LTF) sequence ofa preamble by combining a plurality of interpolating sequences with LTFtone values associated with at least one of the IEEE 802.11n standard orthe IEEE 802.11a standard, wherein the LTF tone values cover at least aportion of bandwidth of a first size, and each of the LTF tone values isrepeated one or more times for different subcarriers, a second circuitconfigured to rotate phases of tones of the LTF sequence per bandwidthof the first size in an effort to reduce a peak-to-average power ratio(PAPR) during a transmission of the LTF sequence, and a third circuitconfigured to replace tones of the LTF sequence at pilot locations witha defined stream of values chosen in an effort to reduce the PAPR.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forconstructing a long training field (LTF) sequence of a preamble bycombining a plurality of interpolating sequences with LTF tone valuesassociated with at least one of the IEEE 802.11n standard or the IEEE802.11a standard, wherein the LTF tone values cover at least a portionof bandwidth of a first size, and each of the LTF tone values isrepeated one or more times for different subcarriers, means for rotatingphases of tones of the LTF sequence per bandwidth of the first size inan effort to reduce a peak-to-average power ratio (PAPR) during atransmission of the LTF sequence, and means for replacing tones of theLTF sequence at pilot locations with a defined stream of values chosenin an effort to reduce the PAPR.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto construct a long training field (LTF) sequence of a preamble bycombining a plurality of interpolating sequences with LTF tone valuesassociated with at least one of the IEEE 802.11n standard or the IEEE802.11a standard, wherein the LTF tone values cover at least a portionof bandwidth of a first size, and each of the LTF tone values isrepeated one or more times for different subcarriers, rotate phases oftones of the LTF sequence per bandwidth of the first size in an effortto reduce a peak-to-average power ratio (PAPR) during a transmission ofthe LTF sequence, and replace tones of the LTF sequence at pilotlocations with a defined stream of values chosen in an effort to reducethe PAPR.

Certain aspects of the present disclosure provide an access point. Theaccess point generally includes at least one antenna, a first circuitconfigured to construct a long training field (LTF) sequence of apreamble by combining a plurality of interpolating sequences with LTFtone values associated with at least one of the IEEE 802.11n standard orthe IEEE 802.11a standard, wherein the LTF tone values cover at least aportion of bandwidth of a first size, and each of the LTF tone values isrepeated one or more times for different subcarriers, a second circuitconfigured to rotate phases of tones of the LTF sequence per bandwidthof the first size in an effort to reduce a peak-to-average power ratio(PAPR) during a transmission of the LTF sequence, a third circuitconfigured to replace tones of the LTF sequence at pilot locations witha defined stream of values chosen in an effort to reduce the PAPR, and atransmitter configured to transmit via the at least one antenna the LTFsequence using a bandwidth of a second size.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates a diagram of a wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates an example block diagram of signal processingfunctions of a physical layer (PHY) of a wireless node in the wirelesscommunications network of FIG. 1 in accordance with certain aspects ofthe present disclosure.

FIG. 3 illustrates a block diagram of an exemplary hardwareconfiguration for a processing system in a wireless node in the wirelesscommunications network of FIG. 1 in accordance with certain aspects ofthe present disclosure.

FIG. 4 illustrates an example structure of preamble comprising a veryhigh throughput long training field (VHT-LTF) sequence in accordancewith certain aspects of the present disclosure.

FIGS. 5A-5J illustrate examples of transmission peak-to-average powerratio (PAPR) results for preferred VHT-LTF sequences constructed for 80MHz channel in accordance with certain aspects of the presentdisclosure.

FIG. 6 illustrates an example VHT-LTF sequence constructed in an effortto reduce PAPR in accordance with certain aspects of the presentdisclosure.

FIG. 7A illustrates an example values at pilot tones of VHT-LTF sequencechosen in an effort to reduce PAPR in accordance with certain aspects ofthe present disclosure.

FIGS. 7B-7I illustrate examples of PAPR results for different VHT-LTFsequences constructed for transmission over 80 MHz channel in accordancewith certain aspects of the present disclosure.

FIGS. 8A-8C illustrate examples of VHT-LTF sequences constructed fortransmission over 80 MHz channel in accordance with certain aspects ofthe present disclosure.

FIG. 9 illustrates example operations that may be performed at awireless node for constructing a VHT-LTF sequence for transmission over80 MHz channel in accordance with certain aspects of the presentdisclosure.

FIG. 9A illustrates example components capable of performing theoperations illustrated in FIG. 9.

FIGS. 10A-10B illustrate examples minimal PAPR results for differentphase rotation patterns applied for constructing Legacy Long TrainingField (L-LTF) and Legacy Short Training Field (L-STF) of a VHTtransmission preamble in accordance with certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein, one skilled in the art should appreciate that thescope of the disclosure is intended to cover any aspect of thedisclosure disclosed herein, whether implemented independently of orcombined with any other aspect of the disclosure. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, the scope of thedisclosure is intended to cover such an apparatus or method which ispracticed using other structure, functionality, or structure andfunctionality in addition to or other than the various aspects of thedisclosure set forth herein. It should be understood that any aspect ofthe disclosure disclosed herein may be embodied by one or more elementsof a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Orthogonal Frequency Division MultipleAccess (OFDMA) systems, Single-Carrier Frequency Division MultipleAccess (SC-FDMA) systems, and so forth. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An SC-FDMA system may utilize interleaved FDMA (IFDMA) totransmit on sub-carriers that are distributed across the systembandwidth, localized FDMA (LFDMA) to transmit on a block of adjacentsub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks ofadjacent sub-carriers. In general, modulation symbols are sent in thefrequency domain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a node implemented in accordance with theteachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known asan access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, or some other terminology. In someimplementations an access terminal may comprise a cellular telephone, acordless telephone, a Session Initiation Protocol (“SIP”) phone, awireless local loop (“WLL”) station, a personal digital assistant(“PDA”), a handheld device having wireless connection capability, orsome other suitable processing device connected to a wireless modem.Accordingly, one or more aspects taught herein may be incorporated intoa phone (e.g., a cellular phone or smart phone), a computer (e.g., alaptop), a portable communication device, a portable computing device(e.g., a personal data assistant), an entertainment device (e.g., amusic or video device, or a satellite radio), a global positioningsystem device, a headset, a sensor or any other suitable device that isconfigured to communicate via a wireless or wired medium. In someaspects the node is a wireless node. Such wireless node may provide, forexample, connectivity for or to a network (e.g., a wide area networksuch as the Internet or a cellular network) via a wired or wirelesscommunication link.

Several aspects of a wireless network will now be presented withreference to FIG. 1. The wireless network 100 is shown with severalwireless nodes, generally designated as nodes 110 and 120. Each wirelessnode is capable of receiving and/or transmitting. In the discussion thatfollows the term “receiving node” may be used to refer to a node that isreceiving and the term “transmitting node” may be used to refer to anode that is transmitting. Such a reference does not imply that the nodeis incapable of performing both transmit and receive operations.

In an aspect of the present disclosure, the wireless network 100 mayrepresent the IEEE 802.11 Wide Local Area Network (WLAN) utilizing theVery High Throughput (VHT) protocol for signal transmissions utilizing acarrier frequency of 5 GHz (i.e., the IEEE 802.11ac specification) orutilizing a carrier frequency of 60 GHz (i.e., the IEEE 802.11adspecification) targeting aggregate throughputs larger than 1 Gigabitsper second. The VHT 5 GHz specification may utilize a wider channelbandwidth, which may comprise two 40 MHz channels for achieving 80 MHzbandwidth, therefore doubling the PHY data rate with negligible increasein cost compared to the IEEE 802.11n standard.

In the detailed description that follows, the term “access point” isused to designate a transmitting node and the term “access terminal” isused to designate a receiving node for downlink communications, whereasthe term “access point” is used to designate a receiving node and theterm “access terminal” is used to designate a transmitting node foruplink communications. However, those skilled in the art will readilyunderstand that other terminology or nomenclature may be used for anaccess point and/or access terminal. By way of example, an access pointmay be referred to as a base station, a base transceiver station, astation, a terminal, a node, an access terminal acting as an accesspoint, or some other suitable terminology. An access terminal may bereferred to as a user terminal, a mobile station, a subscriber station,a station, a wireless device, a terminal, a node or some other suitableterminology. The various concepts described throughout this disclosureare intended to apply to all suitable wireless nodes regardless of theirspecific nomenclature.

The wireless network 100 may support any number of access pointsdistributed throughout a geographic region to provide coverage foraccess terminals 120. A system controller 130 may be used to providecoordination and control of the access points, as well as access toother networks (e.g., Internet) for the access terminals 120. Forsimplicity, one access point 110 is shown. An access point is generallya fixed terminal that provides backhaul services to access terminals inthe geographic region of coverage; however, the access point may bemobile in some applications. In an aspect of the present disclosure, atthe access point 110, a very high throughput long training field(VHT-LTF) sequence may be constructed within a VHT preamble transmittedto one or more of the access terminals 120 such that to achieve apreferred level of peak-to-average power ratio (PAPR) at a transmitterof the access point 110. An access terminal, which may be fixed ormobile, utilizes the backhaul services of an access point or engages inpeer-to-peer communications with other access terminals. Examples ofaccess terminals include a telephone (e.g., cellular telephone), alaptop computer, a desktop computer, a Personal Digital Assistant (PDA),a digital audio player (e.g., MP3 player), a camera, a game console orany other suitable wireless node.

One or more access terminals 120 may be equipped with multiple antennasto enable certain functionality. With this configuration, multipleantennas at the access point 110 may be used to communicate with amultiple antenna access terminal to improve data throughput withoutadditional bandwidth or transmit power. This may be achieved bysplitting a high data rate signal at the transmitter into multiple lowerrate data streams with different spatial signatures, thus enabling thereceiver to separate these streams into multiple channels and properlycombine the streams to recover the high rate data signal.

While portions of the following disclosure will describe accessterminals that also support multiple-input multiple-output (MIMO)technology, the access point 110 may also be configured to supportaccess terminals that do not support MIMO technology. This approach mayallow older versions of access terminals (i.e., “legacy” terminals) toremain deployed in a wireless network, extending their useful lifetime,while allowing newer MIMO access terminals to be introduced asappropriate.

In the detailed description that follows, various aspects of theinvention will be described with reference to a MIMO system supportingany suitable wireless technology, such as Orthogonal Frequency DivisionMultiplexing (OFDM). OFDM is a technique that distributes data over anumber of subcarriers spaced apart at precise frequencies. The spacingprovides “orthogonality” that enables a receiver to recover the datafrom the subcarriers. An OFDM system may implement IEEE 802.11, or someother air interface standard. Other suitable wireless technologiesinclude, by way of example, Code Division Multiple Access (CDMA), TimeDivision Multiple Access (TDMA), or any other suitable wirelesstechnology, or any combination of suitable wireless technologies. A CDMAsystem may implement with IS-2000, IS-95, IS-856, Wideband-CDMA (WCDMA)or some other suitable air interface standard. A TDMA system mayimplement Global System for Mobile Communications (GSM) or some othersuitable air interface standard. As those skilled in the art willreadily appreciate, the various aspects of this invention are notlimited to any particular wireless technology and/or air interfacestandard.

FIG. 2 illustrates a conceptual block diagram illustrating an example ofthe signal processing functions of the Physical (PHY) layer. In atransmit mode, a TX data processor 202 may be used to receive data fromthe Media Access Control (MAC) layer and encode (e.g., Turbo code) thedata to facilitate forward error correction (FEC) at the receiving node.The encoding process results in a sequence of code symbols that that maybe blocked together and mapped to a signal constellation by the TX dataprocessor 202 to produce a sequence of modulation symbols. In an aspectof the present disclosure, the TX data processor 202 may generate a veryhigh throughput long training field (VHT-LTF) sequence within atransmission VHT preamble such that to achieve a preferred level ofPAPR.

In wireless nodes implementing OFDM, the modulation symbols from the TXdata processor 202 may be provided to an OFDM modulator 204. The OFDMmodulator splits the modulation symbols into parallel streams. Eachstream is then mapped to an OFDM subcarrier and then combined togetherusing an Inverse Fast Fourier Transform (IFFT) to produce a time domainOFDM stream.

A TX spatial processor 206 performs spatial processing on the OFDMstream. This may be accomplished by spatially precoding each OFDM andthen providing each spatially precoded stream to a different antenna 208via a transceiver 206. Each transmitter 206 modulates an RF carrier witha respective precoded stream for transmission over the wireless channel.

In a receive mode, each transceiver 206 receives a signal through itsrespective antenna 208. Each transceiver 206 may be used to recover theinformation modulated onto an RF carrier and provide the information toa RX spatial processor 210.

The RX spatial processor 210 performs spatial processing on theinformation to recover any spatial streams destined for the wirelessnode 200. The spatial processing may be performed in accordance withChannel Correlation Matrix Inversion (CCMI), Minimum Mean Square Error(MMSE), Soft Interference Cancellation (SIC) or some other suitabletechnique. If multiple spatial streams are destined for the wirelessnode 200, they may be combined by the RX spatial processor 210.

In wireless nodes implementing OFDM, the stream (or combined stream)from the RX spatial processor 210 is provided to an OFDM demodulator212. The OFDM demodulator 212 converts the stream (or combined stream)from time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate stream for eachsubcarrier of the OFDM signal. The OFDM demodulator 212 recovers thedata (i.e., modulation symbols) carried on each subcarrier andmultiplexes the data into a stream of modulation symbols.

A RX data processor 214 may be used to translate the modulation symbolsback to the correct point in the signal constellation. Because of noiseand other disturbances in the wireless channel, the modulation symbolsmay not correspond to an exact location of a point in the originalsignal constellation. The RX data processor 214 detects which modulationsymbol was most likely transmitted by finding the smallest distancebetween the received point and the location of a valid symbol in thesignal constellation. These soft decisions may be used, in the case ofTurbo codes, for example, to compute a Log-Likelihood Ratio (LLR) of thecode symbols associated with the given modulation symbols. The RX dataprocessor 214 then uses the sequence of code symbol LLRs in order todecode the data that was originally transmitted before providing thedata to the MAC layer.

FIG. 3 illustrates a conceptual diagram illustrating an example of ahardware configuration for a processing system in a wireless node. Inthis example, the processing system 300 may be implemented with a busarchitecture represented generally by bus 302. The bus 302 may includeany number of interconnecting buses and bridges depending on thespecific application of the processing system 300 and the overall designconstraints. The bus links together various circuits including aprocessor 304, machine-readable media 306 and a bus interface 308. Thebus interface 308 may be used to connect a network adapter 310, amongother things, to the processing system 300 via the bus 302. The networkadapter 310 may be used to implement the signal processing functions ofthe PHY layer. In the case of an access terminal 110 (see FIG. 1), auser interface 312 (e.g., keypad, display, mouse, joystick, etc.) mayalso be connected to the bus. The bus 302 may also link various othercircuits such as timing sources, peripherals, voltage regulators, powermanagement circuits, and the like, which are well known in the art, andtherefore, will not be described any further.

The processor 304 is responsible for managing the bus and generalprocessing, including the execution of software stored on themachine-readable media 306. The processor 304 may be implemented withone or more general-purpose and/or special-purpose processors. Examplesinclude microprocessors, microcontrollers, DSP processors and othercircuitry that can execute software. Software shall be construed broadlyto mean instructions, data or any combination thereof, whether referredto as software, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Machine-readable media may include, by way ofexample, RAM (Random Access Memory), flash memory, ROM (Read OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product. The computer-program product may comprisepackaging materials. In an aspect of the present disclosure, theprocessor 304 may perform or direct operations 900 in FIG. 9 and/orother processes for the techniques described herein.

In the hardware implementation illustrated in FIG. 3, themachine-readable media 306 is shown as part of the processing system 300separate from the processor 304. However, as those skilled in the artwill readily appreciate, the machine-readable media 306, or any portionthereof, may be external to the processing system 300. By way ofexample, the machine-readable media 306 may include a transmission line,a carrier wave modulated by data, and/or a computer product separatefrom the wireless node, all which may be accessed by the processor 304through the bus interface 308. Alternatively, or in addition to, themachine readable media 306, or any portion thereof, may be integratedinto the processor 304, such as the case may be with cache and/orgeneral register files.

The processing system 300 may be configured as a general-purposeprocessing system with one or more microprocessors providing theprocessor functionality and external memory providing at least a portionof the machine-readable media 306, all linked together with othersupporting circuitry through an external bus architecture.Alternatively, the processing system 300 may be implemented with an ASIC(Application Specific Integrated Circuit) with the processor 304, thebus interface 308, the user interface 312 in the case of an accessterminal), supporting circuitry (not shown), and at least a portion ofthe machine-readable media 306 integrated into a single chip, or withone or more FPGAs (Field Programmable Gate Array), PLDs (ProgrammableLogic Device), controllers, state machines, gated logic, discretehardware components, or any other suitable circuitry, or any combinationof circuits that can perform the various functionality describedthroughout this disclosure. Those skilled in the art will recognize howbest to implement the described functionality for the processing system300 depending on the particular application and the overall designconstraints imposed on the overall system.

Certain aspects of the present disclosure support a method and apparatusfor constructing a training sequence as a part of VHT transmissionpreamble such that a PAPR at a transmitting node can be sufficientlylow. In an aspect, the training sequence may comprise a VHT-LTFsequence.

Methods of Constructing Long Training Field Sequence for 80 MHz ChannelBandwidth

FIG. 4 illustrates an example structure of a preamble 400 comprising aVHT-LTF sequence in accordance with certain aspects of the presentdisclosure. The preamble 400 may be transmitted from the access point110 to one or more of the access terminals 120 in the wireless network100 illustrated in FIG. 1. The preamble 400 may be transmitted inaccordance with IEEE 802.11ac specification or in accordance with IEEE802.11ad specification.

In an aspect of the present disclosure, the preamble 400 may comprise anomni-legacy portion 402 and a precoded 802.11ac VHT portion 414. Thelegacy portion 402 may comprise: a Legacy Short Training Field (L-STF)404, a Legacy Long Training Field 406, a Legacy Signal (L-SIG) field408, and two OFDM symbols 410, 412 for Very High Throughput Signalfields type A (VHT-SIG-A fields). The VHT-SIG-A fields 410, 412 may betransmitted omni-directionally. The precoded 802.11ac VHT portion 414may comprise: a Very High Throughput Short Training Field (VHT-STF) 416,a Very High Throughput Long Training Field 1 (VHT-LTF1) 418, Very HighThroughput Long Training Fields (VHT-LTFs) 420, a Very High ThroughputSignal field type B (VHT-SIG-B field 422), and a data packet 424. TheVHT-SIG-B field may comprise one OFDM symbol and may be transmittedprecoded/beamformed.

Robust multi-user (MU) MIMO reception may require that the AP transmitsall VHT-LTFs 420 to all supported users. The VHT-LTF sequence 420 mayallow each user to estimate a MIMO channel from all AP antennas to theuser antennas. The user may utilize the estimated channel to performeffective interference nulling from MU-MIMO streams corresponding toother users. In an aspect of the present disclosure, a novel structureof the VHT-LTF sequence 420 may be constructed in an effort to minimize(or at least reduce) PAPR at a transmitter of the AP.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for 80 MHz channel by using four 802.11a LTF sequences in 20MHz sub-bands covered by a complementary sequence, wherein thecomplementary sequence may be equivalent to phase rotation on each ofthe 20 MHz sub-bands. Also, some additional tone values may be chosen inan effort to minimize (or at least reduce) the PAPR during transmissionof the VHT-LTF sequence. Hence, the VHT-LTF pattern may be defined as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{1 - 1},{- 1},1,1,{- 1},1,1,1,1,{{interp}\; 20{Null}}} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{{interp}\; 40{Null}},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,{{interp}\; 20{Null}}} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},{- 1},1,1,1,1,{{interp}\; 20{Null}}} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 40{Null}},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,{{interp}\; 20{Null}}} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (1)\end{matrix}$

It can be observed from equation (1) that there may be at most threezero tone values (subcarriers) around the DC tone, the interpolatingsequences interp20Null, interp40Null, interp80ExtraL, interp80ExtraR maycomprise extra tones to be chosen in an effort to minimize (or at leastreduce) the PAPR, and [c1 c2 c3 c4] may represent the complementarysequence.

By applying various phase rotation patterns on the 20 MHz sub-bands,different PAPR results may be obtained when transmitting VHT-LTFsequences designed based on the VHT-LTF pattern from equation (1). Ingeneral, the VHT-LTF sequences constructed based on four 20 MHz 802.11aLTF sequences may provide improved PAPR results compared to VHT-LTFsequences constructed based on two 802.11n LTF sequences in 40 MHzsub-bands.

It should be noted that phase rotation of upper 40 MHz band may notresult into PAPR reduction; the PAPR results may be even worse. In anaspect, the complementary sequences [1 1 1 −1] and [1 −1 1 1] mayprovide better PAPR results than the complementary sequences [1 1 −1 1]and [−1 1 1 1]. Also, phase rotation by 90 degrees of an odd or even 20MHz sub-band may not help in further PAPR reduction.

The VHT-LTF sequences constructed for 80 MHz channel bandwidth based onthe pattern from equation (1) may provide preferred PAPR results fordifferent non-oversampling and oversampling cases, if the VHT-LTFscomprise the interpolating sequences interp20Null, interp40Null,interp80ExtraL, interp80ExtraR and the rotation pattern [c1 c2 c3 c4] asgiven in FIG. 5A. It should be noted that the label “with rotation” inFIG. 5A and in FIGS. 5B-5J that follows refers to the phase rotation oftones in upper 40 MHz band by 90 degrees, while the label “4×TDI” refersto four times oversampling based on time-domain interpolation (TDI).Sampling rates of 80 Mega-samples per second (Msps) or 320 Msps may beutilized, as illustrated in FIGS. 5A-5J.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones. Thus, in any 20 MHz sub-band,every tone that may be present in 20 MHz 802.11a or in 40 MHz 802.11nmay have the value of corresponding tone from the 20 MHz LTF sequence orthe 40 MHz HT-LTF sequence. In addition, a complementary phase rotationsequence may be applied per 20 MHz 802.11a bandwidth (i.e., 802.11atones may be rotated), and a few missing tones may be filled. In thiscase, the VHT-LTF pattern may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{1 - 1},{- 1},1,1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,{1 - 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{- 1},{- 1},{- 1},1,{{interp}\; 40{Null}},{- 1},1,1,{- 1},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{- 1},{- 1},{- 1},1,{{interp}\; 40{Null}},{- 1},1,1,{- 1},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (2)\end{matrix}$

It can be observed from equation (2) that there may be three zerosubcarriers around the DC tone, the interpolating sequencesinterp40Null, interp80ExtraL, interp80ExtraR may comprise extra tones tobe chosen in an effort to minimize (or at least reduce) the PAPR, and[c1 c2 c3 c4] may represent the complementary phase rotation sequence.One advantage of the VHT-LTF pattern from equation (2) can be that theremay be no need to store different values for existing 20 MHz 802.11a and40 MHz 802.11n tones. On the other hand, a level of PAPR may be slightlyhigher than that of the VHT-LTF pattern from equation (1) because ofless extra tones to be chosen in an effort to minimize (or at leastreduce) the PAPR.

By applying various phase rotation patterns on 20 MHz sub-bands,different PAPR results may be obtained when transmitting 80 MHz VHT-LTFsequences designed based on the VHT-LTF pattern from equation (2). Itcan be observed that the VHT-LTF sequences based on the pattern fromequation (2) may represent a subset of the previously generated VHT-LTFsequences based on the pattern from equation (1). Therefore, PAPRresults of the VHT-LTF sequences constructed based on the pattern fromequation (2) may not be better than PAPR results of the VHT-LTFsequences constructed based on the pattern from equation (1). TheVHT-LTF sequences constructed for 80 MHz channel bandwidth based on thepattern from equation (2) may provide preferred PAPR results fordifferent non-oversampling and oversampling cases, if the VHT-LTFscomprise the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the rotation pattern [c1 c2 c3 c4] as given in FIG.5B.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by slightly modifyingthe VHT-LTF pattern defined by equation (2). All 20 MHz 802.11a tonesand 40 MHz 802.11n tones may be utilized along with the complementaryphase rotation sequence applied on each 20 MHz sub-band (i.e., 20 MHz802.11a tones plus extra data tones of 40 MHz 802.11n). In addition, afew missing tones may be filled. In this case, the VHT-LTF pattern for80 MHz channel may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1}\quad \right.},{{interp}\; 40{Null}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (3)\end{matrix}$

It can be observed from equation (3) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary phase rotation sequence. The VHT-LTFsequences based on the pattern from equation (3) may be different inrotation tone coverage from the VHT-LTF sequences based on equations (1)and (2). One advantage of the VHT-LTF pattern defined by equation (3)can be that there may be no need to store different values for existing20 MHz 802.11a and 40 MHz 802.11n tones. On the other hand, a level ofPAPR may be slightly higher compared to that of the VHT-LTF patterndefined by equation (1) because of less extra tones to be optimized inan effort to minimize (or at least reduce) the PAPR.

The VHT-LTF sequences constructed for 80 MHz channel bandwidth based onthe pattern from equation (3) may provide preferred PAPR results fordifferent non-oversampling and oversampling cases, if the VHT-LTFscomprise the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the rotation pattern [c1 c2 c3 c4] as given in FIG.5C. It can be observed from FIG. 5C that the best PAPR result of 3.2110dB may be obtained, which is better than that of the VHT-LTF sequencebased on the pattern from equation (1) (i.e., the PAPR of 3.2163 dBgiven in FIG. 5A) due to different rotation tone coverage.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all existing20 MHz 802.11a, 20 MHz 802.11n and 40 MHz 802.11n tones with thecomplementary sequence phase rotation applied on each 20 MHz sub-band(i.e., 20 MHz 802.11a tones plus extra data tones of 40 MHz 802.11n) andfilling in a few missing tones. In this case, the VHT-LTF pattern may begiven as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {{- 1},{- 1}} \right\rbrack{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (4)\end{matrix}$

It can be observed from equation (4) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary sequence. The VHT-LTF pattern defined byequation (4) may differ from the VHT-LTF pattern defined by equation (3)in that four extra tones beside interp80ExtraL and interp80ExtraR may befilled by 20 MHz 802.11n LTF values. The VHT-LTF sequences constructedfor 80 MHz channel bandwidth based on the pattern defined by equation(4) may provide preferred PAPR results for various non-oversampling andoversampling cases, if the constructed VHT-LTFs comprise theinterpolating sequences interp40Null, interp80ExtraL, interp80ExtraR andthe rotation pattern [c1 c2 c3 c4] as given in FIG. 5D.

In an aspect of the present disclosure, by modifying the VHT-LTF patterndefined by equation (4), the VHT-LTF sequence may be constructed fortransmission over 80 MHz channel by using all existing 20 MHz 802.11a,20 MHz 802.11n and 40 MHz 802.11n tones, and by utilizing identicalinterpolating sequences interp80ExtraL, interp80ExtraR. In this case,the VHT-LTF pattern may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{1 - 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,{1 - 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {{- 1},{- 1}} \right\rbrack{interp}\; 80{Extra}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (5)\end{matrix}$

It can be observed from equation (5) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp80Extra may comprise extra tones to be chosen in an effort tominimize (or at least reduce) the PAPR, and [c1 c2 c3 c4] may representthe complementary sequence. The VHT-LTF sequences constructed for 80 MHzchannel bandwidth based on the pattern defined by equation (5) mayprovide preferred PAPR results for different non-oversampling andoversampling cases, if the VHT-LTF sequences comprise the interpolatingsequences interp40Null, interp80Extra and the rotation pattern [c1 c2 c3c4] as given in FIG. 5E.

In an aspect of the present disclosure, for 242 subcarriers allocatedfor the VHT-LTF, VHT-LTF pattern starting at subcarrier number −128 ofthe 80 MHz band may comprise a bit sequence 600 illustrated in FIG. 6.The VHT-LTF pattern 600 may utilize at least one of existing 40 MHz802.11n subcarrier values or 20 MHz 80211n subcarrier values (around DConly). This VHT-LTF sequence may require ten extra subcarriers, fouraround DC and six around 40 MHz 802.11n DC subcarriers. Theinterpolating sequences may be given as [Interp40NullL Interp80ExtraLInterp80ExtraR Interp40NullR]={1, −1, −1, −1, −1, 1, −1, 1, 1, −1},wherein first three values may correspond to Interp40NullL, next twovalues may correspond to Interp80ExtraL, next two values may correspondto Interp80ExtraR, and last three values may correspond toInterp40NullR.

One difference between the VHT-LTF sequence 600 and the VHT-LTF patternsdefined by equations (1)-(5) is that three Interp40Null tones may bedifferent for the left and right part of the VHT-LTF sequence 600 (i.e.,for upper and lower 40 MHz band). In an aspect, an extra phase rotationper 20 MHz sub-band may be applied on top of the binary values 600,wherein the phase rotation may correspond to any multiple of 90 degrees.

In an aspect of the present disclosure, the phase rotation pattern {1,1, 1, −1} applied per 20 MHz sub-band may provide a preferred PAPR of4.76 dB using cyclic interpolation and 4-times oversampling. In thiscase, signs of last 64 elements of the sequence 600 may be inverted. Inanother aspect, in order to preserve the 90 degrees phase shift betweenupper and lower 40 MHz sub-channel, a rotation pattern of {1, j, 1, j}may be used with preferred extra ten subcarrier values being {1, −1, 1,−1, −1, 1, −1, −1, −1, −1}.

In an aspect of the present disclosure, different null tone values maybe used for different portions of bandwidth of 80 MHz (i.e., for theupper and lower 40 MHz sub-channels) in the VHT-LTF pattern defined byequation (3). In this case, the VHT-LTF pattern for transmission over 80MHz channel may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{NullL}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{NullR}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (6)\end{matrix}$

It can be observed from equation (6) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp40NullR, interp80ExtraL, interp80ExtraR may comprise extra tonesto be chosen in an effort to minimize (or at least reduce) the PAPR, and[c1 c2 c3 c4] may represent the complementary sequence. The VHT-LTFsequences constructed for 80 MHz channel bandwidth based on the patternfrom equation (6) may provide preferred PAPR results for differentnon-oversampling and oversampling cases, if the VHT-LTF sequencescomprise the interpolating sequences interp40Null, interp40NullR,interp80ExtraL, interp80ExtraR and the phase rotation pattern [c1 c2 c3c4] as given in FIG. 5F.

In an aspect of the present disclosure, different null tone values forthe upper and lower 40 MHz sub-channels may be used in the VHT-LTFpattern defined by equation (3). In this case, the VHT-LTF sequence fortransmission over 80 MHz channel may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{NullL}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{NullR}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (7)\end{matrix}$

It can be observed from equation (7) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp40NullR, interp80ExtraL, interp80ExtraR may comprise extra tonesto be chosen in an effort to minimize (or at least reduce) the PAPR, and[c1 c2 c3 c4] may represent the complementary sequence. The VHT-LTFpattern from equation (7) may be defined in the same way as the VHT-LTFpattern from equation (6), but a different method to generateoversampled sequences with inverse fast Fourier transform (IFFT) of size1024 may be utilized. The VHT-LTF sequences constructed for 80 MHzchannel bandwidth based on the pattern from equation (7) may providepreferred PAPR results for different non-oversampling and oversamplingcases, if the VHT-LTF sequences comprise the interpolating sequencesinterp40Null, interp40NullR, interp80ExtraL, interp80ExtraR and thephase rotation pattern [c1 c2 c3 c4] as given in FIG. 5G.

In an aspect of the present disclosure, by modifying the VHT-LTF patterndefined by equation (2), the VHT-LTF sequence may be also constructedfor 80 MHz channel by using all 20 MHz 802.11a tones and 40 MHz 802.11ntones with the complementary sequence phase rotation applied on each 20MHz sub-band (20 MHz 802.11a plus extra data tones of 40 MHz 802.11n)and filling in a few missing tones. In this case, the VHT-LTF patternfor transmission over 80 MHz channel may be defined as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80{ExtraL}},0,0,0,{{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 40{Null}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (8)\end{matrix}$

It can be observed from equation (8) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary sequence. The VHT-LTF pattern fromequation (8) may be defined in the same way as the VHT-LTF pattern fromequation (3), but a different method to generate oversampled sequenceswith IFFT of size 1024 may be utilized. The VHT-LTF sequencesconstructed for 80 MHz channel bandwidth based on the pattern fromequation (8) may provide preferred PAPR results for differentnon-oversampling and oversampling cases, if the VHT-LTF sequencescomprise the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the phase rotation pattern [c1 c2 c3 c4] as given inFIG. 5H.

In an aspect of the present disclosure, by modifying the VHT-LTF patterndefined by equation (8), the VHT-LTF sequence for transmission over 80MHz channel may be also constructed by using all 40 MHz 802.11n toneswith the complementary sequence phase rotation applied on each 20 MHzsub-band and filling in a few missing tones. In this case, the VHT-LTFpattern for transmission over 80 MHz channel may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{Null}(1)}}} \right\rbrack},{c\; 2.*\left\lbrack {{{interp}\; 40{{Null}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*{interp}\; 80{ExtraL}},0,0,0,{c\; 3.*{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{Null}(1)}}} \right\rbrack},{c\; 4.*\left\lbrack {{{interp}\; 40{{Null}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (9)\end{matrix}$

It can be observed from equation (9) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary sequence. The VHT-LTF sequencesconstructed for 80 MHz channel bandwidth based on the pattern fromequation (9) may provide preferred PAPR results for differentnon-oversampling and oversampling cases, if the VHT-LTF sequencescomprise the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the phase rotation pattern [c1 c2 c3 c4] as given inFIG. 5I.

In an aspect of the present disclosure, different null tone values maybe used for upper and lower 40 MHz sub-bands in the VHT-LTF patterndefined by equation (9). In this case, the VHT-LTF pattern fortransmission over 80 MHz channel may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullL}(1)}}} \right\rbrack},{c\; 2.*\left\lbrack {{{interp}\; 40{{NullL}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*{interp}\; 80{ExtraL}},0,0,0,{c\; 3.*{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullR}(1)}}} \right\rbrack},{c\; 4.*\left\lbrack {{{interp}\; 40{{NullR}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (10)\end{matrix}$

It can be observed from equation (10) that there may be three zerosubcarriers around the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary sequence. The VHT-LTF sequencesconstructed for 80 MHz channel bandwidth based on the pattern fromequation (10) may provide preferred PAPR results for differentnon-oversampling and oversampling cases, if the VHT-LTF sequencescomprise the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the phase rotation pattern [c1 c2 c3 c4] as given inFIG. 5J.

In an aspect of the present disclosure, the VHT-LTF tone values of theVHT-LTF pattern defined by equation (10) may be replaced at pilot toneswith single stream pilot values 700 illustrated in FIG. 7A. In addition,one or more of P values illustrated in FIG. 7B may be applied onnon-pilot tones of the VHT-LTF pattern to provide orthogonality betweendifferent streams of a transmitting node. PAPR results for different Pvalues are also given in FIG. 7B, while 4-times oversampling with IFFTof size 1024 may be applied at the transmitting node. In this case,there may be at most 0.7 dB PAPR fluctuations from one VHT-LTF symbol toanother VHT-LTF symbol and from one transmission stream to another.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones, and utilizing different nulltone values for upper and lower 40 MHz sub-bands. In addition, VHT-LTFtone values at pilot tones may be replaced with the single stream pilots700 from FIG. 7A, the P value of “1” may be applied to non-pilot tones,with filling of missing tones and applying a phase rotation on each 20MHz sub-channel. In this case, the VHT-LTF pattern for transmission over80 MHz channel may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},\lbrack 1\rbrack,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullL}(1)}}} \right\rbrack},{c\; 2.*\left\lbrack {{{interp}\; 40{{NullL}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,\lbrack 1\rbrack,1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},\lbrack 1\rbrack,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*{interp}\; 80{ExtraL}},0,0,0,{c\; 3.*{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,\left\lbrack {- 1} \right\rbrack,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},\left\lbrack {- 1} \right\rbrack,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullR}(1)}}} \right\rbrack},{c\; 4.*\left\lbrack {{{interp}\; 40{{NullR}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,\lbrack 1\rbrack,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},\lbrack 1\rbrack,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (11)\end{matrix}$

A preferred 80 MHz VHT-LTF sequence with the single stream pilots 700from FIG. 7A and the P value of “1” may achieve a PAPR of 4.6138 dB(4-times oversampling with IFFT of size 1024) by using phase rotation[c1 c2 c3 c4]=[−1 1 1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[1 −1, 1, 1 −1 1 1, −1 −1−1 1, 1 −1 1]. The PAPR results are illustrated in FIG. 7C for differentP values.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones, and utilizing different nulltone values for upper and lower 40 MHz sub-bands. In addition, theVHT-LTF tone values at pilot tones may be replaced with the singlestream pilots 700 from FIG. 7A, the P value of “−1” may be applied tonon-pilot tones, with filling of missing tones and applying a phaserotation on each 20 MHz sub-channel. In this case, the VHT-LTF patternused for constructing the VHT-LTF sequences may be defined as inequation (11).

A preferred 80 MHz VHT-LTF sequence with the single stream pilots 700from FIG. 7A and the P value of “−1” may achieve a PAPR of 4.6073 dB(4-times oversampling with IFFT of size 1024) by using phase rotation[c1 c2 c3 c4]=[1 1 −1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[1 −1 1, 1 1 −1 1, 1 −1 11, −1 1 1]. The PAPR results are illustrated in FIG. 7D for different Pvalues.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones, and utilizing different nulltone values for upper and lower 40 MHz sub-bands. In addition, theVHT-LTF tone values at pilot tones may be replaced with the singlestream pilots 700 from FIG. 7A, the P value of exp(−jπ/3) may be appliedto non-pilot tones, with filling of missing tones and applying a phaserotation on each 20 MHz sub-channel. In this case, a base pattern usedfor constructing the VHT-LTF sequences may be defined as in equation(11).

A preferred 80 MHz LTF sequence with the single stream pilots 700 fromFIG. 7A and the P value of exp(−jπ/3) may achieve a PAPR of 4.8658 dB(4-times oversampling with IFFT of size 1024) by using phase rotation[c1 c2 c3 c4]=[−1 1 1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[1 −1 1, 1 −1 −1 1, 1 −11 1, 1 −1 1]. The PAPR results are illustrated in FIG. 7E for differentP values.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones, and utilizing different nulltone values for the upper and lower 40 MHz sub-bands. In addition, theVHT-LTF tone values at pilot tones may be replaced with the singlestream pilots 700 from FIG. 7A, the P value of exp(−j2π/3) may beapplied to non-pilot tones, with filling of missing tones and applying aphase rotation on each 20 MHz sub-channel. In this case, a base patternused for constructing the VHT-LTF sequences may be defined as inequation (11).

A preferred 80 MHz VHT-LTF sequence with the single stream pilots 700from FIG. 7A and the P value of exp(−j2π/3) may achieve a PAPR of 4.8248dB (4-times oversampling with IFFT of size 1024) by using phase rotation[c1 c2 c3 c4]=[1 1 −1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[1 −1 1, 1 1 −1 1, 1 −1 11, −1 1 1]. The PAPR results are illustrated in FIG. 7F for different Pvalues.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones, and utilizing different nulltone values for upper and lower 40 MHz sub-bands. In addition, theVHT-LTF tone values at pilot tones may be replaced with the singlestream pilots 700 from FIG. 7A, the P value of exp(−j4π/3) may beapplied to non-pilot tones, with filling of missing tones and applying aphase rotation on each 20 MHz sub-channel. In this case, a base patternused for constructing the VHT-LTF sequences may be defined as inequation (11).

A preferred 80 MHz VHT-LTF sequence with the single stream pilots 700from FIG. 7A and the P value of exp(−j4π/3) may achieve a PAPR of 4.8248dB (4-times oversampling with IFFT of size 1024) by using phase rotation[c1 c2 c3 c4]=[1 1 −1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[1 −1 1, 1 1 −1 1, 1 −1 11, −1 1 1]. The PAPR results are illustrated in FIG. 7G for different Pvalues.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 20 MHz802.11a tones and 40 MHz 802.11n tones, and utilizing different nulltone values for the upper and lower 40 MHz sub-bands. In addition, theVHT-LTF tone values at pilot tones may be replaced with the singlestream pilots 700 from FIG. 7A, the P value of exp(−j5π/3) may beapplied to non-pilot tones, with filling of missing tones and applying aphase rotation on each 20 MHz sub-channel. In this case, a base patternused for constructing the VHT-LTF sequences may be defined as inequation (11).

A preferred 80 MHz VHT-LTF sequence with the single stream pilots 700from FIG. 7A and the P value of exp(−j5π/3) may achieve a PAPR of 4.8658dB (4-times oversampling with IFFT of size 1024) by using phase rotation[c1 c2 c3 c4]=[−1 1 1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[1 −1 1, 1 −1 −1 1, 1 −11 1, 1 −1 1]. The PAPR results are illustrated in FIG. 7H for differentP values.

In an aspect of the present disclosure, the VHT-LTF sequence may beconstructed for transmission over 80 MHz channel by using all 40 MHz802.11n tones on both 40 MHz sub-channels, wherein the VHT-LTF tonevalues at pilot tones may be replaced with the single stream pilots 700from FIG. 7A, with filling of missing tones and applying a phaserotation on each 20 MHz sub-channel, in an effort to minimize a largestPAPR (i.e., worse case PAPR result) over various P values applied onnon-pilot tones, i.e.:

$\begin{matrix}{{{VHTLTF} = {\min\limits_{S}\left\{ {\max\limits_{P}\left\lbrack {{PAPR}\left( {S_{k},{P\left( {i,j} \right)}} \right)} \right\rbrack} \right\}}},} & (12)\end{matrix}$where S represents all possible VHT-LTF sequences derived from thepattern defined by equation (11). The VHT-LTF sequences for transmissionover 80 MHz channel may be constructed based on the pattern defined inequation (11).

A preferred 80 MHz VHT-LTF sequence may achieve a minimal worse case(maximal) PAPR of 5.0722 dB (4-times oversampling with IFFT of size1024) over various P values by using phase rotation pattern [c1 c2 c3c4]=[−1 1 1 1] and interpolation sequences [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[−1 1 1, −1 −1 1 −1, 1 −1−1 1, 1 −1 1]. The PAPR results are illustrated in FIG. 7I for differentP values.

In an aspect of the present disclosure, the stream of values 700 may notbe applied on pilot tones, while different P values may be applied toall tones of the VHT-LTF pattern defined by equation (11). In this case,PAPR results may be the same as that of the base VHT-LTF sequencewithout applying P values.

In an aspect of the present disclosure, non-pilot tones of the VHT-LTFsequence may be multiplied with one or more P values (i.e., one or moreelements of a P matrix), and pilot tones of the VHT-LTF sequence may bemultiplied with one or more R values (i.e., one or more elements of a Rmatrix). Any applied P value unequal to applied R value may change thebase VHT-LTF sequence. Therefore, different P and R values may lead todifferent PAPR results. Optimization of the VHT-LTF sequence may beperformed by finding a sequence that minimizes a maximal PAPR over allpossible P and R values, i.e.:

$\begin{matrix}{{{VHTLTF} = {\min\limits_{S}\left\{ {\max\limits_{P,R}\left\lbrack {{PAPR}\left( {S,P,R} \right)} \right\rbrack} \right\}}},} & (13)\end{matrix}$where S may represent sequences for all possible extra tone values andphase rotations per 20 MHz sub-bands. In an aspect, the level of PAPRmay only depend on a product of P and R values. For example, {P,R}={exp(jφ),1} and {P, R}={−exp(jφ),−1} may provide the same VHT-LTFsequence rotated by 180 degrees.

In an aspect, optimization of the VHT-LTF sequence may be performedwithout utilizing the single stream values 700 on pilot tones. TheVHT-LTF sequence may be constructed for transmission over 80 MHz channelby utilizing all 40 MHz 802.11n tones on both 40 MHz sub-channels withfilling of missing tones and applying a phase rotation on each 20 MHzsub-channel. In this case, the constructed VHT-LTF pattern may bedefined as:

$\begin{matrix}{{{VHTLTF}_{{- 122},122} = \left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullL}(1)}}} \right\rbrack},{c\; 2.*\left\lbrack {{{interp}\; 40{{NullL}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,{- 1},1,{- 1},1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*{interp}\; 80{ExtraL}},0,0,0,{c\; 3.*{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullR}(1)}}} \right\rbrack},{c\; 4.*\left\lbrack {{{interp}\; 40{{NullR}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}},} & (14)\end{matrix}$where interp40NullL (3 tones), interp80ExtraL (4 tones), interp80ExtraR(4 tones), interp40NullR (3 tones) are extra tones, while interp40NullLand interp40NullR may not need to be identical; [c1 c2 c3 c4] is thephase rotation pattern comprising {+/−1,+/−j} values. Missing tonevalues and the rotation pattern may be optimized for best PAPR.

A preferred VHT-LTF sequence constructed for transmission over 80 MHzchannel based on the pattern defined by equation (14) may achieve a PAPRof 4.48 dB (4-times oversampling with IFFT of size 1024) by using thephase rotation pattern [c1 c2 c3 c4]=[1 1 −1 1], or alternatively [−1 −11 −1], [j j −j j], [−j −j j −j], while the interpolating sequences maybe [interp40NullL, interp80ExtraL, interp80ExtraR, interp40NullR]=[1 11, −1 −1 −1 1, 1 −1 −1 −1, 1 1 −1]. The entire VHT-LTF pattern(excluding phase rotation per 20 MHz sub-channel) is illustrated in FIG.8A, where each row of the bit pattern 802 may correspond to one of thefour 20 MHz sub-channels. The proposed 80 MHz VHT-LTF pattern 802 may be0.24 dB better in PAPR than the optimal pattern from the constraintsearch space assuming equal null tone values for the upper and lower 40MHz sub-bands.

In another aspect of the present disclosure, optimization of the VHT-LTFsequence may be performed by applying the single stream values 700 onpilot tones. The VHT-LTF sequence may be constructed for 80 MHz channelby utilizing all 40 MHz 802.11n tones on both 40 MHz sub-channels,replacing the tone values at pilot tones with the single stream pilots700 from FIG. 7A, with filling of missing tones and applying a phaserotation on each 20 MHz sub-channel. In this case, the constructedVHT-LTF pattern may be defined as:

$\begin{matrix}{{{VHTLTF}_{{- 122},122} = \left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,\left\lbrack {- 1} \right\rbrack,1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{{- 1} - 1},{- 1},1,1,{- 1},{- 1},1,{- 1},\lbrack 1\rbrack,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullL}(1)}}} \right\rbrack},{c\; 2.*\left\lbrack {{{interp}\; 40{{NullL}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,\lbrack 1\rbrack,1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},\lbrack 1\rbrack,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*{interp}\; 80{ExtraL}},0,0,0,{c\; 3.*{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,\left\lbrack {- 1} \right\rbrack,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},\left\lbrack {- 1} \right\rbrack,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullR}(1)}}} \right\rbrack},{c\; 4.*\left\lbrack {{{interp}\; 40{{NullR}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,\lbrack 1\rbrack,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},\lbrack 1\rbrack,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}},} & (15)\end{matrix}$where interp40NullL (3 tones), interp80ExtraL (4 tones), interp80ExtraR(4 tones), interp40NullR (3 tones) are extra tones, while interp40NullLand interp40NullR may not need to be identical; [c1 c2 c3 c4] is thephase rotation pattern comprising {+/−1,+/−j} values. Missing tonevalues and the rotation pattern may be optimized for best PAPR.

A preferred VHT-LTF sequence constructed for transmission over 80 MHzchannel based on the pattern defined by equation (15) may have a minimalworse case PAPR of 5.0722 dB (4-times oversampling with IFFT of size1024) over all P and R values by using the phase rotation pattern [c1 c2c3 c4]=[−1 1 1 1], or alternatively [1 −1 −1 −1], [−j j j j], [j −j −j−j], while the interpolating sequences may be [interp40NullL,interp80ExtraL, interp80ExtraR, interp40NullR]=[−1 1 1, −1 −1 1 −1, −1−1 1, 1 −1 1]. The entire VHT-LTF pattern (excluding phase rotation per20 MHz sub-channel) is illustrated in FIG. 8B, where each row of the bitpattern 804 may correspond to one of the four 20 MHz sub-channels. Forthe preferred VHT-LTF sequence, the product of applied P and R valuesmay be equal to exp(−j2π/3) or exp(−j4π/3).

In yet another aspect of the present disclosure, optimization of theVHT-LTF sequence may be performed by utilizing a new pilot pattern.Pilot values may be the same as the HT-LTF (High Throughput LongTraining Field) values at the pilot tones. In this case, the 80 MHzsubcarrier sequence for VHT-LTF may be constructed by using all 40 MHz802.11n tones on both 40 MHz sub-channels, with filling of missing tonesand applying a phase rotation on each 20 MHz sub-channel. Theconstructed VHT-LTF pattern may be defined as:

$\begin{matrix}{{{VHTLTF}_{{- 122},122} = \left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,\left\lbrack {- 1} \right\rbrack,1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{{- 1} - 1},{- 1},1,1,{- 1},{- 1},1,{- 1},\lbrack 1\rbrack,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullL}(1)}}} \right\rbrack},{c\; 2.*\left\lbrack {{{interp}\; 40{{NullL}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{{- 1} -},1,1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,\left\lbrack {- 1} \right\rbrack,1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},\lbrack 1\rbrack,{- 1},1,1,1,1} \right\rbrack},{c\; 2.*{interp}\; 80{ExtraL}},0,0,0,{c\; 3.*{interp}\; 80{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,\lbrack 1\rbrack,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},\lbrack 1\rbrack,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack,{{interp}\; 40{{NullR}(1)}}} \right\rbrack},{c\; 4.*\left\lbrack {{{interp}\; 40{{NullR}\left( {2,3} \right)}},\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,\lbrack 1\rbrack,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},\lbrack 1\rbrack,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}},} & (16)\end{matrix}$where interp40NullL (3 tones), interp80ExtraL (4 tones), interp80ExtraR(4 tones), interp40NullR (3 tones) are extra tones, while interp40NullLand interp40NullR may not need to be identical; [c1 c2 c3 c4] is thephase rotation pattern comprising {+/−1,+/−j} values. Missing tonevalues and the rotation pattern may be optimized for best PAPR.

A preferred VHT-LTF sequence constructed for transmission over 80 MHzchannel based on the pattern defined by equation (16) may have a minimalworse case PAPR of 5.2070 dB (4-times oversampling with IFFT of size1024) over all P and R values by using the phase rotation [c1 c2 c3c4]=[−1 1 1 1], or alternatively [1 −1 −1 −1], [−j j j j], [j −j −j −j],while the interpolating sequences may be [interp40NullL, interp80ExtraL,interp80ExtraR, interp40NullR]=[1 −1 1, 1 −1 1 −1, 1 −1 −1 1, 1 −1 1].The entire VHT-LTF pattern (excluding phase rotation per 20 MHzsub-channel) is illustrated in FIG. 8C, where each row of the bitpattern 806 may correspond to one of the four 20 MHz sub-channels. Forthe preferred VHT-LTF sequence, the product of applied P and R valuesmay be equal to exp(−j2π/3) or exp(−j4π/3).

FIG. 9 illustrates example operations 900 for constructing the VHT-LTFsequence for transmission over 80 MHz channel in accordance with certainaspects of the present disclosure. In an aspect, the operations 900 maybe performed at the access point 110 of the wireless communicationssystem 100 from FIG. 1. At 902, the VHT-LTF sequence may be constructedby combining a plurality of interpolating sequences with LTF tone valuesassociated with at least one of the IEEE 802.11n wireless communicationsstandard or the IEEE 802.11a wireless communications standard, whereinthe LTF tone values may cover at least a portion of bandwidth of a firstsize, and each of the LTF tone values may be repeated one or more timesfor different subcarriers. At 904, phases of tones of the VHT-LTFsequence may be rotated per bandwidth of the first size (e.g., withdifferent values of c1, c2, c3 and c4 of rotational patterns [c1 c2 c3c4] applied per 20 MHz sub-band) in an effort to minimize (or at leastreduce) PAPR during a transmission of the VHT-LTF sequence. Further,phases of a plurality of tones of the LTF sequence may be rotated in aneffort to reduce the PAPR, wherein the plurality of tones may belong toa portion of the bandwidth of a second size. At 906, tones of theVHT-LTF sequence at pilot locations may be replaced with a stream ofvalues (e.g., with the stream 700 from FIG. 7A) chosen in an effort toreduce the PAPR.

In an aspect of the present disclosure, tones of the VHT-LTF sequence atnon-pilot locations may be multiplied with one or more values (e.g.,P-values), while tones of the VHT-LTF sequence at the pilot locationsmay be multiplied with one or more other values (e.g., R-values),wherein the one or more values and the one or more other values may bedetermined in an effort to reduce a largest PAPR among all PAPR resultsassociated with the transmission of the VHT-LTF sequence.

The constructed VHT-LTF sequence may be transmitted over a wirelesschannel by utilizing the bandwidth of second size. In an aspect of thepresent disclosure, the bandwidth of first size may comprise at leastone of a bandwidth of 20 MHz or a bandwidth of 40 MHz, and the bandwidthof second size may comprise a bandwidth of 80 MHz.

Phase Rotation Pattern for Legacy Part of Preamble

Referring back to FIG. 4, certain aspects of the present disclosuresupport several options for designing the Legacy Long Training Field(L-LTF) 406 and Legacy Short Training Field (L-STF) 404 of the legacypart 402 of the preamble 400 in an effort to reduce PAPR at atransmitting node. The legacy part of preamble may comprise a portion ofthe preamble recognizable by wireless nodes communicating according toprevious, current and future wireless communications standards.

Certain aspects of the present disclosure support several cases how aphase rotation complementary sequence may be designed in an effort toreduce PAPR while transmitting at least on of the L-LTF and L-STF. Inthe first case, the phase rotation pattern may be given as c=[c(1) c(2)c(3) c(4)], where c(i)=1, −1, j, −j. This rotation pattern may havepotential co-existence detection issue, depending on implementation. Inthe second case, the phase rotation pattern may be given as c=[a a*j bb*j], where a, b=1, −1, j, −j. In this case, there may be noco-existence detection issue. In the third case, the phase rotationpattern may be given as c=[1 j e d], where e, d=1, −1, j, −j, exceptd=e*j. This rotation pattern may also have potential co-existencedetection issue, depending on implementation. In the fourth case, thephase rotation pattern may be given as c=[1 j b b*j], where b may be anycomplex number. In this case, there may be no co-existence detectionissues.

FIG. 10A illustrates examples minimal PAPR results for each of theaforementioned four cases of designing the phase rotation pattern forconstructing the L-LTF sequence in accordance with certain aspects ofthe present disclosure. It can be observed from FIG. 10A that the bestPAPR result of 5.3962 dB may be achieved for the phase rotation patternc=[c(1) c(2) c(3) c(4)]=[−1 1 1 1].

FIG. 10B illustrates examples minimal PAPR results for each of theaforementioned four cases of designing the phase rotation pattern forconstructing the L-STF sequence in accordance with certain aspects ofthe present disclosure. It can be observed from FIG. 10B that the bestPAPR result of 4.3480 dB may be achieved for the rotation patternc=[c(1) c(2) c(3) c(4)]=[−1 1 1 1] or c=[c(1) c(2) c(3) c(4)]=[1 1 1−1].

It can be observed from FIGS. 10A-10B that, for both L-LTF and L-STFsequences, the same phase rotation pattern of c=[c(1) c(2) c(3)c(4)]=[−1 1 1 1] may provide the best PAPR result. Further, the phaserotation pattern c=[1 j e d] (i.e., the third case) may result inslightly worse PAPR (i.e., less than 0.2, as given in FIG. 10A and FIG.10B) by using rotation patterns [1 j −1 j] or [1 j 1 −j]. In addition,same phase rotation patterns applied on tones of at least one of theL-STF or the L-LTF (e.g., the phase rotation pattern of c=[−1 1 1 1])may be also applicable to modify phases of tones in at least one of theL-SIG field 408 or the VHT-SIG-A fields 410, 412 of the legacy part 402of the preamble 400 illustrated in FIG. 4 for achieving preferred PAPRresults.

To summarize, the present disclosure provides a method and apparatus forconstructing VHT-LTF sequences for transmission over 80 MHz channel inan effort to provide preferred PAPR results at a transmitting node. TheVHT-LTF sequences may be constructed utilizing at least one of 40 MHz802.11n LTF values, 20 MHz 802.11n LTF values or 20 MHz 802.11a LTFvalues, with appropriately chosen phase rotation per 20 MHz sub-band andwith appropriately chosen extra subcarrier values in an effort tominimize (or at least reduce) PAPR.

The same aforementioned approach for constructing VHT-LTF sequences for80 MHz channel bandwidth may be also used for other numbers ofsubcarriers. In an aspect of the present disclosure, for supporting IEEE802.11ac wireless communication standard, a few tones at band edges maybe zeroed out. In another aspect, all tones around DC may be utilized.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrate circuit (ASIC), or processor. Generally,where there are operations illustrated in Figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, operations 900 illustrated in FIG. 9correspond to components 900A illustrated in FIG. 9A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

For example, the means for constructing may comprise an applicationspecific integrated circuit, e.g., the TX data processor 202 of thewireless node 200 from FIG. 2 or the processor 304 of the processingsystem 300 from FIG. 3. The means for rotating may comprise anapplication specific integrated circuit, e.g., the TX data processor 202of the wireless node 200 or the processor 304 of the processing system300. The means for replacing may comprise an application specificintegrated circuit, e.g., the TX data processor 202 of the wireless node200 or the processor 304 of the processing system 300. The means fortransmitting may comprise a transmitter, e.g., the transceiver 206 ofthe wireless node 200. The means for designing may comprise anapplication specific integrated circuit, e.g., the TX data processor 202of the wireless node 200 or the processor 304 of the processing system300. The means for performing oversampling may comprise a samplingcircuit, e.g., the transceiver 206 of the wireless node 200. The meansfor multiplying may comprise an application specific integrated circuit,e.g., the TX data processor 202 of the wireless node 200 or theprocessor 304 of the processing system 300. The means for utilizing maycomprise an application specific integrated circuit, e.g., the TX dataprocessor 202 of the wireless node 200 or the processor 304 of theprocessing system 300. The means for modifying may comprise anapplication specific integrated circuit, e.g., the TX data processor 202of the wireless node 200 or the processor 304 of the processing system300.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof If implemented in software, thefunctions may be stored or transmitted over as one or more instructionsor code on a computer-readable medium. Computer-readable media includeboth computer storage media and communication media including any mediumthat facilitates transfer of a computer program from one place toanother. A storage medium may be any available medium that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if the software is transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared (IR), radio, and microwave, thenthe coaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, include compactdisc (CD), laser disc, optical disc, digital versatile disc (DVD),floppy disk, and Blu-ray® disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers. Thus, insome aspects computer-readable media may comprise non-transitorycomputer-readable media (e.g., tangible media). In addition, for otheraspects computer-readable media may comprise transitorycomputer-readable media (e.g., a signal). Combinations of the aboveshould also be included within the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method for wireless communications,comprising: constructing, at an apparatus, a long training field (LTF)sequence of a preamble by combining a plurality of interpolatingsequences with LTF tone values, wherein the LTF tone values cover atleast a portion of bandwidth of a first size, and each of the LTF tonevalues is repeated one or more times for different subcarriers; androtating, at the apparatus, phases of tones of the LTF sequence perbandwidth of the first size during a transmission of the LTF sequence.2. The method of claim 1, further comprising: transmitting the LTFsequence within the preamble over a wireless channel by utilizing abandwidth of a second size.
 3. The method of claim 2, wherein thebandwidth of the second size comprises 80 MHz band.
 4. The method ofclaim 1, wherein constructing the LTF sequence comprises: designing theplurality of interpolating sequences in an effort to reduce apeak-to-average-power (PAPR) during the transmission of the LTFsequence.
 5. The method of claim 1, wherein the bandwidth of the firstsize comprises at least one of 20 MHz band or 40 MHz band.
 6. The methodof claim 1, further comprising: rotating phases of a plurality of tonesof the LTF sequence, wherein the plurality of tones belongs to a portionof the bandwidth of the second size.
 7. The method of claim 1, furthercomprising: performing oversampling before transmitting the LTFsequence.
 8. The method of claim 1, wherein the LTF sequence comprisesat most three zero tone values on subcarriers around DC subcarrier. 9.The method of claim 1, further comprising: multiplying tones of the LTFsequence at non-pilot locations with one or more values; and multiplyingtones of the LTF sequence at the pilot locations with one or more othervalues, wherein the one or more values and the one or more other valuesare determined in an effort to reduce a largest peak-to-average powerratio (PAPR) among all PAPR results associated with the transmission ofthe LTF sequence.
 10. The method of claim 1, further comprising:utilizing different null tone values at different portions of abandwidth associated with the transmission of the LTF sequence, whereineach of the portions of bandwidth comprises 40 MHz band.
 11. The methodof claim 1, further comprising: modifying phases of tones of at leastone of a Legacy Long Training Field (L-LTF) or a Legacy Short TrainingField (L-STF) within a legacy part of the preamble using one or morephase rotation patterns, wherein the legacy part of the preamblecomprises a portion of the preamble recognizable by apparatusescommunicating according to previous, current and future wirelesscommunications standards that include at least one of the IEEE 802.11nstandard or the IEEE 802.11a standard.
 12. The method of claim 1,further comprising: modifying phases of tones of a legacy part of thepreamble using one or more phase rotation patterns, wherein the legacypart of the preamble comprises at least one of a Legacy Short TrainingField (L-STF), a Legacy Long Training Field (L-STF), a Legacy Signal(L-SIG) field, or a Very High Throughput Signal field type A(VHT-SIG-A), and the legacy part of the preamble comprises a portion ofthe preamble recognizable by apparatuses communicating according toprevious, current and future wireless communications standards thatinclude at least one of the IEEE 802.11n standard or the IEEE 802.11astandard.
 13. The method of claim 1, wherein the LTF sequence isassociated with the IEEE 802.11ac standard.
 14. The method of claim 1,wherein the LTF sequence comprises the bit pattern:1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1   − 1   − 1  1  1   − 1−1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1  1   − 1  1   − 1  00  0  1   − 1   − 1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1−1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1.15. An apparatus for wireless communications, comprising: a firstcircuit configured to construct a long training field (LTF) sequence ofa preamble by combining a plurality of interpolating sequences with LTFtone values, wherein the LTF tone values cover at least a portion ofbandwidth of a first size, and each of the LTF tone values is repeatedone or more times for different subcarriers; and a second circuitconfigured to rotate phases of tones of the LTF sequence per bandwidthof the first size during a transmission of the LTF sequence.
 16. Theapparatus of claim 15, further comprising: a transmitter configured totransmit the LTF sequence within the preamble over a wireless channel byutilizing a bandwidth of a second size.
 17. The apparatus of claim 16,wherein the bandwidth of the second size comprises 80 MHz band.
 18. Theapparatus of claim 15, wherein the first circuit is also configured to:design the plurality of interpolating sequences in an effort to reduce apeak-to-average- power (PAPR) during the transmission of the LTFsequence.
 19. The apparatus of claim 15, wherein the bandwidth of thefirst size comprises at least one of 20 MHz band or 40 MHz band.
 20. Theapparatus of claim 15, wherein the second circuit is also configured to:rotate phases of a plurality of tones of the LTF sequence, wherein theplurality of tones belongs to a portion of the bandwidth of the secondsize.
 21. The apparatus of claim 15, further comprising: a samplingcircuit configured to perform oversampling before transmitting the LTFsequence.
 22. The apparatus of claim 15, wherein the LTF sequencecomprises at most three zero tone values on subcarriers around DCsubcarrier.
 23. The apparatus of claim 15, further comprising: amultiplier configured to multiply tones of the LTF sequence at non-pilotlocations with one or more values, wherein the multiplier is alsoconfigured to multiply tones of the LTF sequence at the pilot locationswith one or more other values, and the one or more values and the one ormore other values are determined in an effort to reduce a largestpeak-to-average power ratio (PAPR) among all PAPR results associatedwith the transmission of the LTF sequence.
 24. The apparatus of claim15, further comprising: a fourth circuit configured to utilize differentnull tone values at different portions of a bandwidth associated withthe transmission of the LTF sequence, wherein each of the portions ofbandwidth comprises 40 MHz band.
 25. The apparatus of claim 15, furthercomprising: a fourth circuit configured to modify phases of tones of atleast one of a Legacy Long Training Field (L-LTF) or a Legacy ShortTraining Field (L-STF) within a legacy part of the preamble using one ormore phase rotation patterns, wherein the legacy part of the preamblecomprises a portion of the preamble recognizable by apparatusescommunicating according to previous, current and future wirelesscommunications standards that include at least one of the IEEE 802.11nstandard or the IEEE 802.11a standard.
 26. The apparatus of claim 15,further comprising: a fourth circuit configured to modify phases oftones of a legacy part of the preamble using one or more phase rotationpatterns, wherein the legacy part of the preamble comprises at least oneof a Legacy Short Training Field (L-STF), a Legacy Long Training Field(L-STF), a Legacy Signal (L-SIG) field, or a Very High Throughput Signalfield type A (VHT-SIG-A), and the legacy part of the preamble comprisesa portion of the preamble recognizable by apparatuses communicatingaccording to previous, current and future wireless communicationsstandards that include at least one of the IEEE 802.11n standard or theIEEE 802.11a standard.
 27. The apparatus of claim 15, wherein the LTFsequence is associated with the IEEE 802.11ac standard.
 28. Theapparatus of claim 15, wherein the LTF sequence comprises the bitpattern:1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1   − 1   − 1  1  1   − 1−1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1  1   − 1  1   − 1  00  0  1   − 1   − 1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1−1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1.29. An apparatus for wireless communications, comprising: means forconstructing a long training field (LTF) sequence of a preamble bycombining a plurality of interpolating sequences with LTF tone values,wherein the LTF tone values cover at least a portion of bandwidth of afirst size, and each of the LTF tone values is repeated one or moretimes for different subcarriers; and means for rotating phases of tonesof the LTF sequence per bandwidth of the first size during atransmission of the LTF sequence.
 30. The apparatus of claim 29, furthercomprising: means for transmitting the LTF sequence within the preambleover a wireless channel by utilizing a bandwidth of a second size. 31.The apparatus of claim 30, wherein the bandwidth of the second sizecomprises 80 MHz band.
 32. The apparatus of claim 29, wherein the meansfor constructing the LTF sequence comprises: means for designing theplurality of interpolating sequences in an effort to reduce a peak-to-average power ratio (PAPR) during the transmission of the LTFsequence.
 33. The apparatus of claim 29, wherein the bandwidth of thefirst size comprises at least one of 20 MHz band or 40 MHz band.
 34. Theapparatus of claim 29, further comprising: means for rotating phases ofa plurality of tones of the LTF sequence, wherein the plurality of tonesbelongs to a portion of the bandwidth of the second size.
 35. Theapparatus of claim 29, further comprising: means for performingoversampling before transmitting the LTF sequence.
 36. The apparatus ofclaim 29, wherein the LTF sequence comprises at most three zero tonevalues on subcarriers around DC subcarrier.
 37. The apparatus of claim29, further comprising: means for multiplying tones of the LTF sequenceat non-pilot locations with one or more values; and means formultiplying tones of the LTF sequence at the pilot locations with one ormore other values, wherein the one or more values and the one or moreother values are determined in an effort to reduce a largestpeak-to-average power ratio (PAPR) among all PAPR results associatedwith the transmission of the LTF sequence.
 38. The apparatus of claim29, further comprising: means for utilizing different null tone valuesat different portions of a bandwidth associated with the transmission ofthe LTF sequence, wherein each of the portions of bandwidth comprises 40MHz band.
 39. The apparatus of claim 29, further comprising: means formodifying phases of tones of at least one of a Legacy Long TrainingField (L- LTF) or a Legacy Short Training Field (L-STF) within a legacypart of the preamble using one or more phase rotation patterns, whereinthe legacy part of the preamble comprises a portion of the preamblerecognizable by apparatuses communicating according to previous, currentand future wireless communications standards that include at least oneof the IEEE 802.11n standard or the IEEE 802.11a standard.
 40. Theapparatus of claim 29, further comprising: means for modifying phases oftones of a legacy part of the preamble using one or more phase rotationpatterns, wherein the legacy part of the preamble comprises at least oneof a Legacy Short Training Field (L-STF), a Legacy Long Training Field(L-STF), a Legacy Signal (L-SIG) field, or a Very High Throughput Signalfield type A (VHT-SIG-A), and the legacy part of the preamble comprisesa portion of the preamble recognizable by apparatuses communicatingaccording to previous, current and future wireless communicationsstandards that include at least one of the IEEE 802.11n standard or theIEEE 802.11a standard.
 41. The apparatus of claim 29, wherein the LTFsequence is associated with the IEEE 802.11ac standard.
 42. Theapparatus of claim 29, wherein the LTF sequence comprises the bitpattern:1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1   − 1   − 1  1  1   − 1−1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1  1   − 1  1   − 1  00  0  1   − 1   − 1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1−1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1.43. A non-transitory computer-readable medium comprising instructionsexecutable to: construct a long training field (LTF) sequence of apreamble by combining a plurality of interpolating sequences with LTFtone values, wherein the LTF tone values cover at least a portion ofbandwidth of a first size, and each of the LTF tone values is repeatedone or more times for different subcarriers; and rotate phases of tonesof the LTF sequence per bandwidth of the first size during atransmission of the LTF sequence.
 44. The non-transitorycomputer-readable medium of claim 43, wherein the LTF sequence isassociated with the IEEE 802.11ac standard.
 45. The non-transitorycomputer-readable medium of claim 43, wherein the LTF sequence comprisesthe bit pattern:1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1   − 1   − 1  1  1   − 1−1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1  1   − 1  1   − 1  00  0  1   − 1   − 1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1−1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1.46. An access point, comprising: at least one antenna; a first circuitconfigured to construct a long training field (LTF) sequence of apreamble by combining a plurality of interpolating sequences with LTFtone values, wherein the LTF tone values cover at least a portion ofbandwidth of a first size, and each of the LTF tone values is repeatedone or more times for different subcarriers; a second circuit configuredto rotate phases of tones of the LTF sequence per bandwidth of the firstsize during a transmission of the LTF sequence; and a transmitterconfigured to transmit via the at least one antenna the LTF sequencewithin the preamble over a wireless channel by utilizing a bandwidth ofa second size.
 47. The access point of claim 46, wherein the LTFsequence is associated with the IEEE 802.11ac standard.
 48. The accesspoint of claim 46, wherein the LTF sequence comprises the bit pattern:1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1   − 1   − 1  1  1   − 1−1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1  1   − 1  1   − 1  00  0  1   − 1   − 1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1−1   − 1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1   − 1   − 1   − 1  1  1−1  1   − 1  1  1   − 1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1  1  1  1  1  1   − 1   − 1  1  1   − 1  1   − 1  1   − 1   − 1   − 1−1   − 1  1  1   − 1   − 1  1   − 1  1   − 1  1  1  1  1.49. A non-transitory machine readable storage medium configured to storea preamble having a long training field (LTF) sequence, wherein the LTFsequence comprises: a plurality of interpolating sequences combined withLTF tone values that cover at least a portion of bandwidth of a firstsize, wherein each of the LTF tone values is repeated one or more timesfor different subcarriers; and a complementary sequence equivalent tophase rotation on each portion of the bandwidth of the first size. 50.The non-transitory machine readable storage medium recited in claim 49,wherein the bandwidth of the first size comprises at least one of a 20MHz band or a 40 MHz band.
 51. The non-transitory machine readablestorage medium recited in claim 49, wherein the LTF sequence furthercomprises: non-pilot tones multiplied with one or more first values,wherein pilot tones are multiplied with one or more second values. 52.The non-transitory machine readable storage medium recited in claim 49,wherein the LTF sequence further comprises: different null tone valuesat different portions of a bandwidth used to transmit the LTF sequence,wherein each of the portions of the bandwidth comprises a 40 MHz band.53. The non-transitory machine readable storage medium recited in claim49, wherein the preamble further comprises a legacy portion thatincludes one or more tones having phases that are modified according toone or more phase rotation patterns.
 54. A method for wirelesscommunications, comprising: transmitting a preamble to one or morereceiving nodes over a multiple-input multiple- output (MIMO) wirelesschannel, wherein the preamble comprises a long training field (LTF)sequence having a plurality of interpolating sequences combined with LTFtone values that cover at least a portion of bandwidth of a first sizeand a complementary sequence equivalent to phase rotation on eachportion of the bandwidth of the first size, and wherein each of the LTFtone values is repeated one or more times for different subcarriers; androtating phases of tones of the LTF sequence per bandwidth of the firstsize according to the complementary sequence during the transmitting.55. An apparatus for wireless communications, comprising: a transmitterconfigured to transmit a preamble to one or more receiving nodes over amultiple-input multiple-output (MIMO) wireless channel, wherein thepreamble comprises a long training field (LTF) sequence having aplurality of interpolating sequences combined with LTF tone values thatcover at least a portion of bandwidth of a first size and acomplementary sequence equivalent to phase rotation on each portion ofthe bandwidth of the first size, and wherein each of the LTF tone valuesis repeated one or more times for different subcarriers; and at leastone processor configured to rotate phases of tones of the LTF sequenceper bandwidth of the first size according to the complementary sequenceduring transmission of the preamble.
 56. An apparatus for wirelesscommunications, comprising: means for transmitting a preamble to one ormore receiving nodes over a multiple-input multiple-output (MIMO)wireless channel, wherein the preamble comprises a long training field(LTF) sequence having a plurality of interpolating sequences combinedwith LTF tone values that cover at least a portion of bandwidth of afirst size and a complementary sequence equivalent to phase rotation oneach portion of the bandwidth of the first size, and wherein each of theLTF tone values is repeated one or more times for different subcarriers;and means for rotating phases of tones of the LTF sequence per bandwidthof the first size according to the complementary sequence duringtransmission of the preamble.
 57. A non-transitory computer-readablemedium comprising instructions executable to: transmit a preamble to oneor more receiving nodes over a multiple-input multiple-output (MIMO)wireless channel, wherein the preamble comprises a long training field(LTF) sequence having a plurality of interpolating sequences combinedwith LTF tone values that cover at least a portion of bandwidth of afirst size and a complementary sequence equivalent to phase rotation oneach portion of the bandwidth of the first size, and wherein each of theLTF tone values is repeated one or more times for different subcarriers;and rotate phases of tones of the LTF sequence per bandwidth of thefirst size according to the complementary sequence during transmissionof the preamble.
 58. A method for wireless communications, comprising:receiving a preamble from a transmitting node over a multiple-inputmultiple-output (MIMO) wireless channel, wherein the received preamblecomprises a long training field (LTF) sequence having a plurality ofinterpolating sequences combined with LTF tone values that cover atleast a portion of bandwidth of a first size and a complementarysequence equivalent to phase rotation on each portion of the bandwidthof the first size, and wherein each of the LTF tone values is repeatedone or more times for different subcarriers; and estimating the MIMOwireless channel from the transmitting node based at least in part onthe LTF sequence in the received preamble.
 59. An apparatus for wirelesscommunications, comprising: a receiver configured to receive a preamblefrom a transmitting node over a multiple- input multiple-output (MIMO)wireless channel, wherein the received preamble comprises a longtraining field (LTF) sequence having a plurality of interpolatingsequences combined with LTF tone values that cover at least a portion ofbandwidth of a first size and a complementary sequence equivalent tophase rotation on each portion of the bandwidth of the first size, andwherein each of the LTF tone values is repeated one or more times fordifferent subcarriers; and at least one processor configured to estimatethe MIMO wireless channel from the transmitting node based at least inpart on the LTF sequence in the received preamble.
 60. An apparatus forwireless communications, comprising: means for receiving a preamble froma transmitting node over a multiple-input multiple- output (MIMO)wireless channel, wherein the received preamble comprises a longtraining field (LTF) sequence having a plurality of interpolatingsequences combined with LTF tone values that cover at least a portion ofbandwidth of a first size and a complementary sequence equivalent tophase rotation on each portion of the bandwidth of the first size, andwherein each of the LTF tone values is repeated one or more times fordifferent subcarriers; and means for estimating the MIMO wirelesschannel from the transmitting node based at least in part on the LTFsequence in the received preamble.
 61. A non-transitorycomputer-readable medium comprising instructions executable to: receivea preamble from a transmitting node over a multiple-inputmultiple-output (MIMO) wireless channel, wherein the received preamblecomprises a long training field (LTF) sequence having a plurality ofinterpolating sequences combined with LTF tone values that cover atleast a portion of bandwidth of a first size and a complementarysequence equivalent to phase rotation on each portion of the bandwidthof the first size, and wherein each of the LTF tone values is repeatedone or more times for different subcarriers; and estimate the MIMOwireless channel from the transmitting node based at least in part onthe LTF sequence in the received preamble.